1. Field of the Invention
The present invention relates to carbodiimide- and uretonimine-isocyanurate-containing polyisocyanates, to the process for the preparation thereof and to microcellular foams and elastomers prepared from said modified polyisocyanate compositions. More particularly, the invention relates to polyisocyanate compositions containing carbodiimide and uretonimine and isocyanurate linkages prepared by reacting organic polyisocyanates in the presence of catalysts which convert isocyanate groups to carbodiimide groups and in the presence of catalysts which promote the trimerization of isocyanate groups to isocyanurate.
2. Description of the Prior Art
Carbodiimide- and uretonimine-containing isocyanates are known in the prior art and have been prepared employing a variety of processes. Further, isocyanurate-modified polyisocyanate compositions and processes for the preparation thereof have been reported. Rigid low density foams containing carbodiimide and isocyanurate linkages are known. Among the references which can be cited are the following: U.S. Pat. No. 4,085,140 which discloses a process for the conversion of isocyanate groups to carbodiimide groups employing a co-catalyst system. U.S. Pat. No. 4,031,026 teaches a diphenylmethane diisocyanate composition which comprises diphenylmethane diisocyanate, a diphenylmethane diisocyanate uretonimine group containing derivative, a reaction product of MDI of the diphenylmethane diisocyanate and a diol, and methylene bridged polyphenol polyisocyanate. U.S. Pat. No. 3,996,223 teaches a process for the production of organic polyisocyanates containing isocyanurate structure by polymerizing said organic polyisocyanate in the presence of catalysts which cause the formation of trimers. U.S. Pat. No. 3,657,161 claims a polycarbodiimide polyisocyanurate foam and a process for preparing the same which comprises polymerizing an organic polyisocyanate in the presence of a blowing agent, a catalyst which promotes the formation of carbodiimide groups and a catalyst which promotes the simultaneous formation of isocyanurate groups. U.S. Pat. No. 4,085,140 teaches the preparation of carbodiimide-containing polyisocyanates suitable for the preparation of microcellular foams or elastomers. Applicants are unaware of any art which teaches or even suggests the compositions and process for the preparation thereof of stable liquid polyisocyanate compositions which contain both carbodiimide or uretonimine and isocyanurate linkages and the foams prepared therefrom.